This invention relates to a bottom-blown steel making process.
One well-known steel making process involves refining pig iron by top or bottom blowing with oxygen. When bottom blowing is employed, a sheath of hydrocarbon shielding fluid, such as propane, natural gas or light oil is injected in surrounding relation to the oxygen in order to prolong tuyere and refractory life. Because solid iron bearing materials, such as scrap and prereduced pelletized iron are relatively cheaper than hot metal, it is often desirable in such processes to employ a solid charge to the extent possible. The percentage of solid metal to hot metal charge is generally limited by the heat generated during the exothermic reactions between the oxygen and impurities in the hot metal, such as carbon, silicon, phosphorous and manganese.
The proportion of solid charge may be increased somewhat by using the bottom tuyeres as preheating burners. Such tuyeres generally include an inner pipe for carrying oxygen and a second pipe spaced from the inner pipe to provide an outer annulus for delivering the hydrocarbon shielding fluid. In such tuyeres, the area of the gap between the pipes is relatively much smaller than the area of the inner oxygen carrying pipe because the volume of shielding fluid required during normal operation is only about 2-4% of the volume of oxygen. This severely restricts the capacity of such tuyeres to act as preheating burners because the relatively small area of the outer annulus severly limits the quantity of hydrocarbon that can be provided for preheating. One attempt to increase the hydrocarbon available for preheating involves the use of a dual supply system for providing hydrocarbon in liquid form during preheating and in gaseous form during refining. This system, while satisfactory, complicates the fluid delivery system which normally passes through the vessel's trunnion pins.
A steel making process which would permit an increase in the percentage of solid furnace charge without the necessity for special fluid delivery systems would be an advancement in the art.